The present invention relates to cylinders for an automatic transmission, and more particularly, to the cylinders including a disk-like return spring.
One of the cylinders of this type is described, for example, in MITSUBISHI HEAVY INDUSTRIES Technical Report, Vol. 21 No. 1 published in January 1984. This cylinder comprises a multiplate brake arranged on the inner peripheral surface of a transmission casing and a hydraulic servomechanism arranged on the left of the multiplate brake for controlling operation of the brake. The hydraulic servomechanism comprises a cylinder formed with a support wall of the inner peripheral surface of the transmission casing, a piston slidably disposed in the cylinder, a disk-like return spring interposed between the piston and a frictional coupling member of the multiplate brake and having an annular inclined face.
With the above cylinder, however, the piston presses the frictional coupling member of the multiplate brake through the return spring, so that when hydraulic oil with a predetermined pressure is supplied to a hydraulic chamber defined by the cylinder and the piston upon engagement of the brake, the piston is moved immediately, whereas as being pressed through the return spring, the frictional coupling member has a response lag by elastic deformation of the return spring.
Moreover, since the return spring comprises a single leaf spring having an annular inclined face, adjustment of the characteristic of the leaf spring needs to change the thickness thereof. This requires full replacement of the leaf spring, i.e. provision of various return springs having characteristic adjusted, leading to the increased number of parts.
It is, therefore, an object of the present invention to provide cylinders for an automatic transmission, which contribute to an enhancement in the response characteristic of a mechanism to be actuated by a piston and a facilitation of adjustment of a disk-like return spring.
The present invention provides generally a structure for an automatic transmission wherein a mechanism is arranged in a casing having an inner periphery formed with a spline, the structure comprising: a cylinder; a piston slidably arranged in the cylinder, the piston actuating the mechanism; a return spring that biases the piston, the return spring comprising an annular portion abutting on the piston and a plurality of leaf-spring portions protruding outward equiangularly from an outer periphery of the annular portion and having a front end engaged with the spline of the casing; and a plurality of pressing portions formed with the piston, the pressing portions abutting on the mechanism through clearances between the leaf-spring portions of the return spring.